The present invention relates generally to the protection of metallic surfaces from corrosion. The invention addresses prevention of corrosion of metallic surfaces with environmentally less damaging inhibitors.
It is a known fact that many oil and gas producing formations yield hydrocarbon, brine, carbon dioxide and/or hydrogen sulfide, which are very corrosive on metal tubing, pumps, casing and other production equipment. This is especially true of metal surfaces, which are exposed to aqueous solutions along with other corrosive chemicals. Corrosion is higher in wells producing brine containing a high percentage of dissolved acidic gases such as carbon dioxide or hydrogen sulfide and inorganic salts, or low molecular weight organic acids such as acetic formic or propionic acid. These chemical ingredients dissolved in water at elevated temperature increases the corrosivity of the medium.
Traditionally, the most common way to reduce corrosion is to add a corrosion inhibitor to a corrosive system to preserve metals. Inhibitors of the corrosion metals are chemical compounds and formulations of these which, when present in small quantities in an aggressive medium, inhibit corrosion by bringing about changes in the surface condition of the metal. The commercially available corrosion inhibitors are less friendly to the environment. Increasingly, operating companies, the government and the public have become concerned about toxicity and environment impact of oil field chemicals, especially in offshore. In offshore operations such as in North Sea, environmentally sounds chemicals are very important. To protect marine environment, corrosion inhibitor should be non-toxic to fish, plants and organisms, and should be biodegradable and reasonably water soluble (it is desired that the partition coefficient of octanol and water should be less than three). Furthermore, the flash point of the solvent and the solvent evaporating factor of the chemical are considered in designing these inhibitors.
For this, corrosion inhibitors, the inventive focus has been a corrosion inhibitors, which have low toxicity in a marine environment. The present invention is related to compounds and compositions, which are very effective corrosion inhibitors in oil and gas field applications, and have less impact on the natural environment.
The low toxicity inhibitor of the present disclosure finds application in tropical waters where the temperature remains relatively high around the offshore production platform. Likewise, it can be used in colder waters including the North Sea and elsewhere. These are waters where temperatures get down to freezing, and yet still support different types of marine life. In both instances, the corrosion inhibitor of the present disclosure is a fluid which can be discharged with the salt water and yet have low toxicity for the marine life.
In general terms, the present disclosure sets forth a reaction product, which is obtained by a relatively straight forward reaction and does not involve extreme difficulties in manufacture.
Consider a production situation in which a production stream of oil droplets suspended in salt water is recovered at 185xc2x0 F. This is not an uncommon circumstance. This stream will be produced up through the production tubing string in the well, and it is then directed through the well head equipment, a set of valves enabling connection to horizontal gathering lines that extend to a separator tank. A separator tank is commonly a tall, relatively thin upstanding cylinder. It is sometimes called a shotgun tank. Depending on the volume, the tank may be 20 to 30 feet in height. Again, depending on the volume, the diameter may be as small as about 3 feet up to some large diameter. With the passage of time, the oil collects on the top surface of accumulated liquid, and the hot salt water collects at the bottom. While it may cool in that interval, and may actually become quite cool dependent on the northern latitude of the tank and the season of the year, the interior of the tank is exposed to strong salt water solutions, often at elevated temperatures. It is necessary to protect against corrosion the production tubing stream, the well head equipment, and everything made of metal which comes into contact with the flowing fluid. While at the first blush it might appear that produced oil is relatively benign, this is far from the situation that normally occurs. Rather, the produced fluid is typically quite corrosive and will react to damage the metal surfaces.
In some instances, an offshore production platform will produce a large quantity of salt water along with the produced oil. The separator tank on the platform is filled substantially with produced salt water. The salt water can be returned to the ocean, or perhaps to an injection well. In some instances, return of this to the ocean is the only practical solution. Where the produced mix of fluids includes a lot of salt water, and the salt water is returned to the ocean, the operator is placed in a pinch by the desirability of returning produced salt water back to the ocean which does not create a pollution risk, and on the other hand, the pinch relates to the need to add corrosion inhibitors. Successful corrosion inhibitors have been provided heretofore which are quite good and are exemplified in the U.S. Pat. Nos. 5,611,991, 5,611,992, and 5,779,938. These inhibitors are quite successful. They are, however, not readily discharged into a ocean or other salt water environment. Effectively, these inhibitors are handicapped by being somewhat toxic to marine life. The present invention set out an inhibitor compound, more accurately, a family of compounds which has reduced toxicity. Effectively, toxic compounds which include fatty amines, fatty poly amines, fatty amides, fatty poly amides, imidazolines and poly imidazolines are all reacted with both acrylic acid and monochloro acetic acid in such a way that the base nitrogen atoms present in these compounds are reacted with acrylic acid and monochloro acetic acid, or their salts. This converts a highly toxic base molecule (being an amine as exemplified above) and yields a product which provides a quality corrosion inhibitor but which is less toxic.
The need for corrosion inhibitors is accelerated when a well produces something other than the expected flowing oil (with out without natural gas). Often, salt water is produced as mentioned. In addition to that in liquid form, added gases are produced which sometimes create problems. These added gases include CO2 and H2S. Small bubbles of these two gases are often entrained in the produced oil at substantial depths, and the bubbles, while not readily apparent at great depths where the pressure reduces bubble size, become something of a problem as the containment pressure is reduced while flowing to the surface. At the surface, what would appear to be a flowing stream of liquid becomes a froth as the dissolved gases come out of solution, thereby exposing the pipe to corrosion. These gases create problems, thereby shortening the life of the metal goods. Effectively, this attacks the production tubing and any other metal exposed to the flow. The flowing produced oil, with or without the above mentioned gases, and with or without bubbles of entrained natural gas, may also occasionally include low molecular weight organic acids. These are exemplified by acids such as acetic, formic and propionic acid. These acids will attack any exposed metal surface.
Inhibitors can be provided that overcome the problems just mentioned which are grouped in three general groups, the problems derived from: 1) produced gases; 2) produced salt water; and 3) produced acids. The concentration or amount of each may vary, but these are especially problematic depending on pH of the flow, temperature, relative concentrations, and the intervals between servicing of the well. For instance, it is necessary to service the well by adding the corrosion inhibitor exemplified by this present disclosure to the flow periodically. Without adding it in the flow, protection is lost.
Moreover, this poses a significant problem in offshore locations where the produced salt water is separated from the valuable products and is ultimately returned to the ocean. This is permitted provided the salt water discharge back into the ocean is nontoxic to the aquatic life in the ocean. The toxicity of the discharge obviously relates to something other than the salt content in the discharge. The ocean itself, being already charged to a specified salt solution, can receive various and sundry types of saltwater discharges from an offshore production platform. However, those discharges pose a problem if they attack the small fishes or other life that normally inhabits such waters. While this may be somewhat dependent on local salinity levels and ambient temperature, the present disclosure sets forth a corrosion inhibitor and a method for making the inhibitor, to provide an inhibitor which can be discharged in the presence of marine life without damage. An example of this will be given including a number of tests using specific, common, marine life.
The low toxicity inhibitor of the present disclosure finds application in tropical waters where the temperature remains relatively high around the offshore production platform. Likewise, it can be used in colder waters including the North Sea and elsewhere. These are waters where the temperatures get down to freezing, and yet still support different types of marine life. In both instances, the corrosion inhibitor of the present disclosure is a fluid which can be discharged with the salt water and yet have low toxicity for the marine life.
In general terms, the present disclosure sets forth a reaction product which is obtained by a relatively simple reaction. As will be detailed, the reactive sequence is relatively straight forward and does not involve extreme difficulties in manufacture. Furthermore, the reactive process permits use of several different feeds within a specified group of feed stocks.
This disclosure is directed to the synthesis of the corrosion inhibitor which is effective to protect ferrous metals, and yet which dissolves in produced petroleum streams with or without salt water, and is ultimately soluble in salt water. It has a low toxicity for marine life when discharged into the ocean. This low toxicity level protects marine life in the vicinity of the discharge.
The context of present disclosure is protection of metal surfaces exposed to flowing produced oil and gas products beginning with the production well and including the well equipment. This is exemplified the production tubing stream which extends from a production zone, appropriate gas lift valves and well head equipment at the top of the well. This includes the gathering lines which extend from the well head to a tank battery or a separator tank. This also includes the metal surfaces which contact produced fluids and other well head located equipment such as separators, high pressure pumps, and the like. This also extends to the gathering lines and the storage tanks. A common location is on an offshore production platform where the fluids flow from one or more wells into the production equipment and produced salt water is separated and ultimately returning to the ocean. One aspect of the corrosion inhibitor is that it has a very mild, almost benign impact on marine life in the ocean.
The corrosion inhibitor of the present disclosure is a corrosion inhibitor which is added to a flowing production stream. The stream that carries the corrosive material also carries the inhibitor. The inhibitor contacts and coats the metal. The exposed metal, being coated by the flowing stream, prevents subsequent corrosion of the surface by the corrosive agents in the flowing stream. As mentioned in the background above, the flowing stream is typically a flow of produced oil from a well which includes one or more of the typical corrosive agents noted above and including: 1) inorganic salts mixed in water, hence brine; 2) dissolved gases (other than natural gas) which are commonly CO2 or H2S or both; and 3) dissolved acids exemplified by acetic, formic or propionic acids. These corrosive agents may be present or absent, may be present in dilute or strong concentrations, and may be highly irregular in flow rate. Suffice it to say, when they are typically present, they attack the metal of the production flow path beginning literally with the producing zone and extending up through the production tubing and down stream ultimately to a tank battery for storage.
The present corrosion inhibitor is an amine derivative which is represented by any of the following three formulas:
Rxe2x80x94X(C2H4NZ)nC2H4NZ2;xe2x80x83xe2x80x83(1)
or
Z2N(CH2)mNZ2;xe2x80x83xe2x80x83(2)
or
Rxe2x80x94NZ2;xe2x80x83xe2x80x83(3)
where
R=C12 to a C36 hydrocarbon or aryl saturated or unsaturated ring;
X=amide (xe2x80x94COxe2x80x94NHxe2x80x94) or a 5-membered cyclic imidazoline ring;
Z=unsaturated carboxylic acid or halocarboxylic acid, or salts of these compounds;
n=an integer from 1 to 6; and
m=an integer from 12 to 36.
One method of manufacture of compounds within the above 20 definition is obtained by reacting at least one mole of unsaturated carboxylic acid with one mole of halocarboxylic acid, preferably monochloro acetic acid or salts thereof.
Common procedures within the above generalized definition include the production of the corrosion inhibitor by reacting alkyl amine, aryl, amine, polyethyl amine with C12 to C36 fatty acid, and subsequently reacting with halocarboxylic acid, preferably monochloro acetic acid (MCAA), and an unsaturated carboxylic acid, preferably acrylic acid (AA) or their salts, in such a way that all reactive hydrogen atoms, attached to the nitrogen atoms, are substituted with a least one molecule of MCAA and one molecule of AA.
Among the amines which are suitable for this invention are: ethylene diamine, ethylene triamine, triethylene, tetramine, aminoethyl, ethanol amine, tetraethylene pentamine, aminoethyl piperazine, cocoamine, cocodiamine, tallow amine, tallow diamine and tallow triamine.
The fatty acid may include: tall oil fatty acid, oleic acid, linoleic acid, coconut acid, tallow acid and naphthenic acid.
A common mode of testing the effectiveness of a corrosion inhibitor involves the use of a rotating cylinder electrode. This standardized test device is used to make measurements which are evaluated using a linear polarization resistance technique (LPR hereinafter) in which a test coupon is monitored for the duration of the test. The test coupon is mounted in the test equipment, and then scans are made from +15 mv to xe2x88x9215 mv versus the open circuit potential. The scan is made at a rate of about 0.5 mv per second using commercially available test equipment with a commercially available software package. The equipment measures and generates the results automatically. The test is carried out in NACE brine (100,000 TDS) which brine is deoxygenated. It is purged continuously with CO2, and the test is carried out at an elevated temperature of 160xc2x0 F. The electrode is rotated at 3,000 rpm which is equivalent to a fluid velocity of 6 ft/sec (a flow rate common in production tubing strings). Several examples are given below. In the table, the headings for the table include the example number (listed below), the composition of the corrosion inhibitor is listed next, and the data especially tabulates the corrosion rate. The corrosion rate is normally indicated in mills per year, see the column labeled MPY Corrosion. Each test composition is tabulated in table 1 to indicate the molar equivalent of MCAA or AA. In addition, the table shows relative concentrations of the corrosion inhibitor in either of two ranges which are 25 to 50 or 50 to 100 parts/million or ppm and effect on the marine line, discussed below after several examples are given.